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<h1 id="es6"><a href="#es6" class="headerlink" title="es6"></a>es6</h1><h2 id="类"><a href="#类" class="headerlink" title="类"></a>类</h2><p>在es6中可以使用 <code>class</code> 关键字声明一个类，后面可以使用这个类进行实例化。<br>语法：</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">class</span> <span class="title class_">NameOfClass</span> &#123;</span><br><span class="line">    <span class="comment">// class body</span></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<h2 id="类-constructor-构造函数"><a href="#类-constructor-构造函数" class="headerlink" title="类 constructor 构造函数"></a>类 constructor 构造函数</h2><p>用于传递参数然后返回实例对象，使用 <code>new</code> 关键字时自动使用这个构建函数。比如:</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">class</span> <span class="title class_">Game</span> &#123;</span><br><span class="line">    <span class="title function_">constructor</span>(<span class="params">name, type, price</span>) &#123;</span><br><span class="line">        <span class="variable language_">this</span>.<span class="property">name</span> = name;</span><br><span class="line">        <span class="variable language_">this</span>.<span class="property">type</span> = type;</span><br><span class="line">        <span class="variable language_">this</span>.<span class="property">price</span> = price;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> residentEvil = <span class="keyword">new</span> <span class="title class_">Game</span>(<span class="string">&#x27;Resident Evil 3&#x27;</span>, <span class="string">&#x27;AVG&#x27;</span>, <span class="string">&#x27;414￥&#x27;</span>);</span><br></pre></td></tr></table></figure>

<h2 id="类中公用方法"><a href="#类中公用方法" class="headerlink" title="类中公用方法"></a>类中公用方法</h2><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">class</span> <span class="title class_">Game</span> &#123;</span><br><span class="line">    <span class="comment">// constructor和上面一样</span></span><br><span class="line">    <span class="title function_">describe</span>(<span class="params"></span>) &#123;</span><br><span class="line">        <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="string">&#x27;游戏名：&#x27;</span> + <span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">        <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="string">&#x27;游戏类型：&#x27;</span> + <span class="variable language_">this</span>.<span class="property">type</span>);</span><br><span class="line">        <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="string">&#x27;游戏售价：&#x27;</span> + <span class="variable language_">this</span>.<span class="property">price</span>);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> residentEvil = <span class="keyword">new</span> <span class="title class_">Game</span>(<span class="string">&#x27;Resident Evil 3&#x27;</span>, <span class="string">&#x27;AVG&#x27;</span>, <span class="string">&#x27;414￥&#x27;</span>);</span><br><span class="line">residentEvil.<span class="title function_">describe</span>();</span><br></pre></td></tr></table></figure>

<h2 id="类的继承"><a href="#类的继承" class="headerlink" title="类的继承"></a>类的继承</h2><p>子类可以继承父类的属性和方法</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 父类</span></span><br><span class="line"><span class="keyword">class</span> <span class="title class_">Game</span> &#123;</span><br><span class="line">    <span class="title function_">constructor</span>(<span class="params"></span>) &#123;</span><br><span class="line">        <span class="comment">// ...</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="title function_">price</span>(<span class="params"></span>) &#123;</span><br><span class="line">        <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="string">&#x27;游戏价格：100￥&#x27;</span>);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">class</span> <span class="title class_">AVGGame</span> <span class="keyword">extends</span> <span class="title class_ inherited__">Game</span> &#123;</span><br><span class="line"></span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> son = <span class="keyword">new</span> <span class="title class_">AVGGame</span>();</span><br><span class="line">son.<span class="title function_">price</span>();</span><br></pre></td></tr></table></figure>

<h2 id="super-关键字"><a href="#super-关键字" class="headerlink" title="super 关键字"></a>super 关键字</h2><p><code>super</code> 关键字用于访问父类和调用父类上的函数（构造函数和普通函数）。比如：</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">class</span> <span class="title class_">Game</span> &#123;</span><br><span class="line">    <span class="title function_">constructor</span>(<span class="params">name, price</span>) &#123;</span><br><span class="line">        <span class="variable language_">this</span>.<span class="property">name</span> = name;</span><br><span class="line">        <span class="variable language_">this</span>.<span class="property">price</span> = price;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="title function_">getPrice</span>(<span class="params"></span>) &#123;   </span><br><span class="line">        <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="string">&#x27;游戏售价：&#x27;</span> + <span class="variable language_">this</span>.<span class="property">price</span>);</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="title function_">retName</span>(<span class="params"></span>) &#123;</span><br><span class="line">        <span class="keyword">return</span> <span class="variable language_">this</span>.<span class="property">name</span>;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">class</span> <span class="title class_">AVGGame</span> <span class="keyword">extends</span> <span class="title class_ inherited__">Game</span> &#123;</span><br><span class="line">    <span class="title function_">constructor</span>(<span class="params">name, price</span>) &#123;</span><br><span class="line">        <span class="variable language_">super</span>(name, price);</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="title function_">getName</span>(<span class="params"></span>) &#123;</span><br><span class="line">        <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">super</span>.<span class="title function_">retName</span>());</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> residentEvil = <span class="keyword">new</span> <span class="title class_">AVGGame</span>(<span class="string">&#x27;Resident Evil 3&#x27;</span>,<span class="string">&#x27;414￥&#x27;</span>);</span><br><span class="line">residentEvil.<span class="title function_">getPrice</span>();</span><br><span class="line">residentEvil.<span class="title function_">getName</span>();</span><br></pre></td></tr></table></figure>
<blockquote>
<p>注意：super必须要在this之前</p>
</blockquote>
<h2 id="三个注意点"><a href="#三个注意点" class="headerlink" title="三个注意点"></a>三个注意点</h2><ol>
<li>在ES6中类没有变量提升，需要先定义后使用。</li>
<li>类里面共有的属性和方法要加this进行使用，比如<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">class</span> <span class="title class_">Game</span> &#123;</span><br><span class="line">    <span class="title function_">constructor</span>(<span class="params">name, price</span>) &#123;</span><br><span class="line">        <span class="variable language_">this</span>.<span class="property">name</span> = name;</span><br><span class="line">        <span class="variable language_">this</span>.<span class="property">price</span> = price;</span><br><span class="line">        <span class="variable language_">this</span>.<span class="property">fn</span> = <span class="variable language_">this</span>.<span class="property">getPrice</span>;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="title function_">getPrice</span>(<span class="params"></span>) &#123;   </span><br><span class="line">        <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="string">&#x27;游戏售价：&#x27;</span> + <span class="variable language_">this</span>.<span class="property">price</span>);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></li>
<li>类里的this指向问题：谁调用某个方法，那么那个方法里面的this指向的是调用者，而构建函数指向的是实例化的对象。</li>
</ol>
<h1 id="es5"><a href="#es5" class="headerlink" title="es5"></a>es5</h1><h2 id="创建对象方法"><a href="#创建对象方法" class="headerlink" title="创建对象方法"></a>创建对象方法</h2><p>创建对象有三种方法：</p>
<ol>
<li>对象字面量</li>
<li>new Object();</li>
<li>自定义构造函数<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 1.</span></span><br><span class="line"><span class="keyword">var</span> obj1 = &#123;&#125;;</span><br><span class="line"><span class="comment">// 2.</span></span><br><span class="line"><span class="keyword">var</span> obj2 = <span class="keyword">new</span> <span class="title class_">Object</span>();</span><br><span class="line"><span class="comment">// 3. </span></span><br><span class="line"><span class="keyword">function</span> <span class="title function_">Game</span>(<span class="params">name</span>) &#123;</span><br><span class="line">    <span class="variable language_">this</span>.<span class="property">name</span> = name;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> gta = <span class="keyword">new</span> <span class="title class_">Game</span>(<span class="string">&#x27;Grand Theft Auto&#x27;</span>);</span><br></pre></td></tr></table></figure></li>
</ol>
<h2 id="实例成员和静态成员"><a href="#实例成员和静态成员" class="headerlink" title="实例成员和静态成员"></a>实例成员和静态成员</h2><p>实例成员只能通过实例化对象来访问，比如上面 <code>Game</code> 中的name，不可以直接通过 <code>Game.name</code> 访问。而静态成员是在构造函数本身上添加的成员，可以同构造函数访问但是不能通过实例对象进行访问，比如在上面的代码基础上：</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="title class_">Game</span>.<span class="property">name</span>); <span class="comment">//undefined</span></span><br><span class="line"><span class="title class_">Game</span>.<span class="property">type</span> = <span class="string">&#x27;AVG&#x27;</span>;</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="title class_">Game</span>.<span class="property">type</span>); <span class="comment">//AVG</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(gta.<span class="property">type</span>);  <span class="comment">//undefined</span></span><br></pre></td></tr></table></figure>
<h2 id="构造函数原型-prototype"><a href="#构造函数原型-prototype" class="headerlink" title="构造函数原型 prototype"></a>构造函数原型 prototype</h2><p>如果在构造函数中把函数赋值给实例对象，会因为每次实例化对象时都会分配空间给相同的对象，所以会造成空间浪费，这时候就需要用到原型了。</p>
<p>构造函数通过原型分配的函数是所有对象共享的。</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 同样是上面的代码</span></span><br><span class="line"><span class="title class_">Game</span>.<span class="property"><span class="keyword">prototype</span></span>.<span class="property">getName</span> = <span class="keyword">function</span>(<span class="params"></span>) &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> gta = <span class="keyword">new</span> <span class="title class_">Game</span>(<span class="string">&#x27;Grand Theft Auto&#x27;</span>);</span><br><span class="line">gta.<span class="title function_">getName</span>();  <span class="comment">//Grand Theft Auto</span></span><br></pre></td></tr></table></figure>
<p>这样上面的 <code>getName</code> 就不用每次实例化对象时都分配一段空间给这个函数。</p>
<h2 id="对象原型-proto"><a href="#对象原型-proto" class="headerlink" title="对象原型 proto"></a>对象原型 <strong>proto</strong></h2><p>上面实例化对象可以使用 <code>getName</code> 是因为对象中有一个 <code>__proto__</code> 对象，他等价于构造函数的 <code>prototype</code> ，所以只有构造函数的原型中有这个方法就可以在实例对象中使用</p>
<h2 id="constructor-构造函数"><a href="#constructor-构造函数" class="headerlink" title="constructor 构造函数"></a>constructor 构造函数</h2><p>对象原型 <code>__proto__</code> 和 构造函数原型 <code>prototype</code> 里面都有一个constructor属性，同时指回构造函数本身。</p>
<h2 id="继承父类的属性"><a href="#继承父类的属性" class="headerlink" title="继承父类的属性"></a>继承父类的属性</h2><p>这里需要用到 <code>call</code> 调用父类的构造函数。</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">function</span> <span class="title function_">Father</span>(<span class="params">name</span>) &#123;</span><br><span class="line">    <span class="variable language_">this</span>.<span class="property">name</span> = name;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">function</span> <span class="title function_">Son</span>(<span class="params">name</span>) &#123;</span><br><span class="line">    <span class="title class_">Father</span>.<span class="title function_">call</span>(<span class="variable language_">this</span>, name)</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> son = <span class="keyword">new</span> <span class="title class_">Son</span>(<span class="string">&#x27;son&#x27;</span>);</span><br></pre></td></tr></table></figure>

<h2 id="继承父类的方法"><a href="#继承父类的方法" class="headerlink" title="继承父类的方法"></a>继承父类的方法</h2><p>根据原型链的原理，只需要实例化一个父类的对象赋值给子类对象的 <code>prototype</code> 就可以通过原型链访问到父类的方法了。</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">function</span> <span class="title function_">Father</span>(<span class="params">name</span>) &#123;</span><br><span class="line">    <span class="variable language_">this</span>.<span class="property">name</span> = name;</span><br><span class="line">&#125;</span><br><span class="line"><span class="title class_">Father</span>.<span class="property"><span class="keyword">prototype</span></span>.<span class="property">getName</span> = <span class="keyword">function</span>(<span class="params"></span>) &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">function</span> <span class="title function_">Son</span>(<span class="params">name</span>) &#123;</span><br><span class="line">    <span class="title class_">Father</span>.<span class="title function_">call</span>(<span class="variable language_">this</span>, name);</span><br><span class="line">&#125;</span><br><span class="line"><span class="title class_">Son</span>.<span class="property"><span class="keyword">prototype</span></span> = <span class="keyword">new</span> <span class="title class_">Father</span>();</span><br><span class="line"><span class="keyword">var</span> son = <span class="keyword">new</span> <span class="title class_">Son</span>(<span class="string">&#x27;son&#x27;</span>);</span><br><span class="line">son.<span class="title function_">getName</span>();  <span class="comment">// son</span></span><br></pre></td></tr></table></figure>


<h1 id="类的本质"><a href="#类的本质" class="headerlink" title="类的本质"></a>类的本质</h1><p>在es6之前可以通过构造函数+原型实现面向对象编程，es6之后可以通过类进行面向对象编程。类其实可以看做是构造函数和原型结合的语法糖。</p>

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